implement new for simplified grammar

src/main/java/de/hsrm/compiler/Klang/Klang.java

@@ -19,7 +19,8 @@ public class Klang {
     KlangParser parser = new KlangParser(tokens);
 
     ParseTree tree = parser.parse(); // begin parsing at init rule
-    EvalVisitor visitor = new EvalVisitor();
-    visitor.visit(tree);
+    Visitor visitor = new Visitor();
+    int result = visitor.visit(tree);
+    System.out.println(result);
   }
 }

src/main/java/de/hsrm/compiler/Klang/Visitor.java

@@ -0,0 +1,19 @@
+package de.hsrm.compiler.Klang;
+
+public class Visitor extends KlangBaseVisitor<Integer> {
+    @Override
+    public Integer visitMultiplicativeExpr(KlangParser.MultiplicativeExprContext ctx) {
+        int result = 1;
+        
+        for (var expr: ctx.unaryExpression()) {
+            result *= this.visit(expr);
+        }
+        
+        return result;
+    }
+    
+    @Override
+    public Integer visitUnaryExpression(KlangParser.UnaryExpressionContext ctx) {
+        return Integer.parseInt(ctx.getText());
+    }
+}